Abstract

Aminoglycoside antibiotics are used to treat life-threatening bacterial infections but can cause deafness due to hair cell death in the inner ear. Compounds have been described that protect zebrafish lateral line hair cells from aminoglycosides, but few are effective in the cochlea. As the aminoglycosides interact with several ion channels, including the mechanoelectrical transducer (MET) channels by which they can enter hair cells, we screened 160 ion-channel modulators, seeking compounds that protect cochlear outer hair cells (OHCs) from aminoglycoside-induced death in vitro. Using zebrafish, 72 compounds were identified that either reduced loading of the MET-channel blocker FM 1-43FX, decreased Texas red–conjugated neomycin labeling, or reduced neomycin-induced hair cell death. After testing these 72 compounds, and 6 structurally similar compounds that failed in zebrafish, 13 were found that protected against gentamicin-induced death of OHCs in mouse cochlear cultures, 6 of which are permeant blockers of the hair cell MET channel. None of these compounds abrogated aminoglycoside antibacterial efficacy. By selecting those without adverse effects at high concentrations, 5 emerged as leads for developing pharmaceutical otoprotectants to alleviate an increasing clinical problem.

Figure 5

Representative MET currents from OHCs in cultures prepared from P2 pups recorded before, during, and after exposure to (A) 50 μM 13143 (n = 12) and (B) 50 μM 13222 (n = 6). MET currents were recorded at membrane potentials from –164 mV to +96 mV in response to a sine-wave stimulus. Current-voltage curves for the peak MET currents derived from the recordings shown in A and B demonstrate (C) the lack of interaction of 13143 with the channel and (D) the voltage-dependence of block by 13222. (E) Fractional block of the MET currents at all membrane potentials reveals that 7 compounds, including 13143, do not interact with the channel. (F) Six compounds, including 13222, provide a voltage-dependent block that is in most cases strongest at moderately negative potentials. Error bars are SEM. Numbers of independent tests are shown after each compound number in graphs (E and F).